This invention relates generally to igniter materials such as for use in inflatable restraint systems and, more specifically, to porous igniter materials such as for use in devices, systems and methods used in the inflation of an automotive safety restraint system inflatable vehicle occupant restraint airbag cushion.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag,” that is inflated or expanded with gas when the vehicle encounters a sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an “inflator.”
Many types of inflator devices have been disclosed in the art for use in inflating one or more inflatable restraint system airbag cushions. Many prior art inflator devices include a solid form of gas generant material which is burned to produce or form gas used in the inflation of an associated airbag cushion.
Such inflator devices tend to involve a chain of reactions of materials, e.g., pyrotechnics, contained within an inflator device to produce or generate an inflation medium, e.g., inflation gas, to result in the deployment of an airbag cushion. For example, such devices commonly employ a squib or initiator which is electrically ignited when a collision is sensed. The discharge from the squib in turn ignites or lights an igniter material. The igniter material desirably burns relatively rapidly, with a large caloric output, such as to desirably relatively uniformly ignite a supply of gas generant material. The gas generant material in turn bums to produce or form gas such as is directed into the airbag cushion to effect inflation thereof. In general, the ballistic properties of a gas generant material are controlled by the shape (usually tablets or wafers) and burn rate of the gas generant.
As will be appreciated, rapid and repeatable ignition of a gas generant material is critical to providing inflator devices that enable an airbag cushion to reliably deploy in the very short periods of time associated with vehicle occupant passive restraint installations. For example, inflator designers typically require the period of time following actuation till gas expelled from an inflator can be measured to be less than 3 milliseconds.
Inflator design attempts to incorporate a simply mixing or blending together of an igniter powder with gas generant tablets, wafers, or other gas generant particle shapes have generally not proven successful. In particular, igniter powders in such inflator designs over time tend to be susceptible to migration away from the squib and the gas generant particles. Consequently, such designs may experience unacceptable ignition delays and produce or result in less than optimal occupant protection.
In view thereof, conventional inflator devices have commonly employed some form of igniter material packaging to ensure the proper placement and positioning of the igniter material to effect desired ignition and reaction of the associated gas generant material. More specifically, it is common for inflator devices to employ a powdered igniter material that is packaged within the inflator in close proximity to the squib and to the gas generant. In such an arrangement, the squib is able to rapidly light the igniter material and the burning igniter material powder expels hot particles and gas such as to cause or result in uniform and rapid ignition of the gas generant material.
In practice, the packaging of such igniter materials can be relatively simple and straightforward such as by packaging the igniter material in a small canister, such as made of aluminum, in the center of a toroidal-shaped driver inflator or relatively complex such as by packaging the igniter material in a tubular device which in turn is inserted down a bore of a stack of gas generant wafers in a typical, cylindrically-shaped passenger inflator device. Regardless of the specifics of such designs, the packaging of a powdered igniter material within an inflator device has typically required the inclusion of additional parts and added weight as well as increased assembly and manufacture expense.
An alternative approach has been to press the igniter material into a particle shape with similar dimensions as the gas generant particles and to strategically position these igniter material particles within the gas generant mass in close proximity to the squib. Specific examples of this approach include: igniter material wafers placed or positioned at the end of a gas generant wafer stack next to a squib or placed in a regular periodicity along the length of a gas generant wafer stack; igniter material tablet(s) at the squib end of a bed of gas generant tablets in a side impact inflator; igniter material tablets place down a bore of a gas generant wafer stack; igniter material tablets placed in the center of a bed of gas generant tablets in a toroidal driver inflator; or other similar concepts. Unfortunately, pressed igniter particles typically have a greatly reduced surface area as compared to a similar mass of igniter powder. As will be appreciated, a reduced surface area of the igniter material during combustion will typically result in a reduced rate of energy release therefrom and may therefore cause or result in undesired ignition delays within an airbag inflator device.
In view of the above, there is a need and a demand for an igniter material body that has dimensions similar to those of gas generant particles but which igniter material body provides or results in a surface area similar to those of powdered igniter materials.